Cascode amplifier segmentation for enhanced thermal ruggedness

ABSTRACT

According to some implementation, a power amplifier includes a plurality of pairs of transistors, each pair of transistors including a common emitter transistor and a common base transistor arranged in a cascode configuration. The power amplifier further includes electrical connections implemented to connect the plurality of pairs in a parallel configuration between an input node and an output node. According to some implementations, the electrical connections are configured to distribute a collector current to all of the common base transistors to thereby reduce likelihood of damage to one or more common base transistors during a thermal run-away event.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority to U.S. Provisional Application No.62/116,508 filed Feb. 15, 2015, entitled CASCODE AMPLIFIER SEGMENTATIONFOR ENHANCED THERMAL RUGGEDNESS, the disclosure of which is herebyexpressly incorporated by reference herein in its entirety.

BACKGROUND

Field

The present disclosure relates to power amplifiers in radio-frequency(RF) applications.

Description of the Related Art

Many devices, such as wireless devices, require or utilize a cascodeamplifier structure to decouple performance-degrading thermal protectionsolutions from high performance radio-frequency (RF) power arrayelements.

In some applications, thermal ruggedness can be built into an array byincreasing distances between devices in the power array, and by throughballasting techniques. Such techniques can introduce local feedback ateach of the devices within the power array.

Spreading of the array can reduce the heating of adjacent array elementsand can effectively reduce the thermal resistance of the array to heatsinking structures. Such a technique can result in an increased area forthe array, and can also increase the corresponding die size and cost.

Ballasting techniques are often in the form of emitter degeneration orbase degeneration. These solutions can introduce loss in the RF signalpath which can degrade gain, efficiency and saturated power, therebyreducing performing. Other solutions which utilize a cascodearchitecture may include a common connection of the cascode emitters,which typically involves ballasting of the cascode devices to preventthermal run-away.

SUMMARY

In accordance with a number of implementations, the present disclosurerelates to a power amplifier including a plurality of pairs oftransistors, each pair of transistors including a common emittertransistor and a common base transistor arranged in a cascodeconfiguration. The power amplifier further includes electricalconnections implemented to connect the plurality of pairs in a parallelconfiguration between an input node and an output node, the electricalconnections configured to distribute a collector current to all of thecommon base transistors to thereby reduce likelihood of damage to one ormore common base transistors during a thermal run-away event.

In some implementations, for each of the plurality of pairs oftransistors, the emitter of the common emitter transistor is coupled tothe base of the common base transistor through a bypass capacitance.

In some implementations, for each of the plurality of pairs oftransistors, the base of the common emitter transistor is coupled to aninput bias circuit. In some implementations, the input bias circuitincludes a radio-frequency (RF) ballast resistance. In someimplementations, the input bias circuits of the plurality of pairs oftransistors are coupled a common RF input.

In some implementations, for each of the plurality of pairs oftransistors, the emitter of the common emitter transistor is coupled toa ground potential.

In some implementations, for each of the plurality of pairs oftransistors, the base of the common base transistor is coupled to acascode bias circuit. In some implementations, the cascode bias circuitincludes a cascode ballast resistance.

In some implementations, for each of the plurality of pairs oftransistors, the collector of the common base transistor is coupled to asupply voltage.

In some implementations, the collectors of the common base transistorsof the plurality of pairs of transistors are coupled to yield a commonRF output.

In some implementations, the present disclosure relates to aradio-frequency (RF) module that includes a packaging substrateconfigured to receive a plurality of components. The RF module furtherincludes a power amplification system implemented on the packagingsubstrate, the power amplification system including a power amplifier(PA) configured to receive and amplify an RF signal. The PA includes aplurality of pairs of transistors, each pair of transistors including acommon emitter transistor and a common base transistor arranged in acascode configuration. The PA further includes electrical connectionsimplemented to connect the plurality of pairs in a parallelconfiguration between an input node and an output node, the electricalconnections configured to distribute a collector current to all of thecommon base transistors to thereby reduce likelihood of damage to one ormore common base transistors during a thermal run-away event.

In accordance with some implementations, the PA of the RF moduleincludes the functions and/or features of any of the PAs and/oramplification systems described herein.

According to some teachings, the present disclosure relates to aradio-frequency (RF) device that includes a transceiver generate to anRF signal. The RF device also includes a front-end module (FEM) incommunication with the transceiver, the FEM includes a packagingsubstrate configured to receive a plurality of components. The FEMfurther includes a power amplifier (PA) configured to and amplify the RFsignal. The PA includes a plurality of pairs of transistors, each pairof transistors including a common emitter transistor and a common basetransistor arranged in a cascode configuration. The PA further includeselectrical connections implemented to connect the plurality of pairs ina parallel configuration between an input node and an output node, theelectrical connections configured to distribute a collector current toall of the common base transistors to thereby reduce likelihood ofdamage to one or more common base transistors during a thermal run-awayevent. THE RF device further includes an antenna in communication withthe FEM, the antenna configured to transmit the amplified RF signal.

In some implementations, the RF device includes a wireless device. Insome implementations, the wireless device is a cellular phone.

In accordance with some implementations, the PA of the FEM moduleincludes the functions and/or features of any of the PAs and/oramplification systems described herein.

For purposes of summarizing the disclosure, certain aspects, advantagesand novel features of the inventions have been described herein. It isto be understood that not necessarily all such advantages may beachieved in accordance with any particular embodiment of the invention.Thus, the invention may be embodied or carried out in a manner thatachieves or optimizes one advantage or group of advantages as taughtherein without necessarily achieving other advantages as may be taughtor suggested herein.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the present disclosure can be understood in greater detail, amore particular description may be had by reference to the features ofvarious implementations, some of which are illustrated in the appendeddrawings. The appended drawings, however, merely illustrate the morepertinent features of the present disclosure and are therefore not to beconsidered limiting, for the description may admit to other effectivefeatures.

FIG. 1 is a block diagram of a wireless system or architecture accordingto some implementations.

FIG. 2 is a block diagram of an amplification system according to someimplementations.

FIGS. 3A-3E shows schematic diagrams of power amplifiers according tosome implementations.

FIG. 4 is a block diagram of an amplification system according to someimplementations.

FIG. 5A is a schematic diagram of an array of cascoded devices accordingto some implementations.

FIG. 5B shows an example collector current path through the array ofcascoded devices in FIG. 5A according to some implementations.

FIG. 6 is a schematic diagram of an isolated cascode array according tosome implementations.

FIG. 7 is a schematic diagram of a cascoded device according to someimplementations.

FIG. 8 is a schematic diagram of an array of two cascoded devicesaccording to some implementations.

FIG. 9 is an example layout of a common emitter (CE)/common base (CB)pair and related connections forming a cascoded device according to someimplementations.

FIG. 10 is an example layout of two CE/CB pairs and related connectionsforming cascoded devices according to some implementations.

FIG. 11 is an example layout of CE/CB pairs in a two-dimensional arrayaccording to some implementations.

FIG. 12 shows temperature-rise curves as a function of device spacingaccording to some implementations.

FIG. 13 shows amplitude-to-amplitude (AM-AM) distortion performanceplots at various operating conditions according to some implementations.

FIG. 14 shows amplitude-to-phase (AM-PM) distortion performance plots atvarious operating conditions according to some implementations.

FIG. 15 shows performance plots of collector efficiency versus outputpower and power added efficient versus out power at various operatingconditions according to some implementations.

FIG. 16 shows an enlarged view of the performance plots in FIG. 15according to some implementations.

FIG. 17 shows performance plots of adjusted channel leakage ratio(ACLR1) curves as a function of output power according to someimplementations.

FIG. 18 shows an enlarged view of the performance plots in FIG. 17according to some implementations.

FIG. 19 shows performance plots of ACLR2 curves as a function of outputpower according to some implementations.

FIG. 20 is a schematic diagram of an example radio-frequency (RF) moduleaccording to some implementations.

FIG. 21 is a schematic diagram of an example RF device according to someimplementations.

In accordance with common practice the various features illustrated inthe drawings may not be drawn to scale. Accordingly, the dimensions ofthe various features may be arbitrarily expanded or reduced for clarity.In addition, some of the drawings may not depict all of the componentsof a given system, method or device. Finally, like reference numeralsmay be used to denote like features throughout the specification andfigures.

DETAILED DESCRIPTION OF SOME IMPLEMENTATIONS

The headings provided herein, if any, are for convenience only and donot necessarily affect the scope or meaning of the claimed invention.

Referring to FIG. 1, one or more features of the present disclosuregenerally relate to a wireless system or architecture 50 having anamplification system 52. In some embodiments, the amplification system52 can be implemented as one or more devices, and such device(s) can beutilized in the wireless system/architecture 50. In some embodiments,the wireless system/architecture 50 can be implemented in, for example,a portable wireless device. Examples of such a wireless device aredescribed herein.

FIG. 2 shows that the amplification system 52 of FIG. 1 typicallyincludes a radio-frequency (RF) amplifier assembly 54 having one or morepower amplifiers (PAs). In the example of FIG. 2, three PAs 60 a-60 care depicted as forming the RF amplifier assembly 54. It will beunderstood that other numbers of PA(s) can also be implemented. It willalso be understood that one or more features of the present disclosurecan also be implemented in RF amplifier assemblies having other types ofRF amplifiers.

In some embodiments, the RF amplifier assembly 54 can be implemented onone or more semiconductor die, and such die can be included in apackaged module such as a power amplifier module (PAM) or a front-endmodule (FEM). Such a packaged module is typically mounted on a circuitboard associated with, for example, a portable wireless device.

The PAs (e.g., 60 a-60 c) in the amplification system 52 are typicallybiased by a bias system 56. Further, supply voltages for the PAs aretypically provided by a supply system 58. In some embodiments, either orboth of the bias system 56 and the supply system 58 can be included inthe foregoing packaged module having the RF amplifier assembly 54.

In some embodiments, the amplification system 52 can include a matchingnetwork 62. Such a matching network can be configured to provide inputmatching and/or output matching functionalities for the RF amplifierassembly 54.

For the purpose of description, it will be understood that each PA (60)of FIG. 2 can be implemented in a number of ways. FIGS. 3A-3E shownon-limiting examples of how such a PA can be configured. FIG. 3A showsan example PA having an amplifying transistor 64, where an input RFsignal (RF_in) is provided to a base of the transistor 64, and anamplified RF signal (RF_out) is output through a collector of thetransistor 64.

FIG. 3B shows an example PA having a plurality of amplifying transistors(e.g., 64 a, 64 b) arranged in stages. An input RF signal (RF_in) isprovided to a base of the first transistor 64 a, and an amplified RFsignal from the first transistor 64 a is output through its collector.The amplified RF signal from the first transistor 64 a is provided to abase of the second transistor 64 b, and an amplified RF signal from thesecond transistor 64 b is output through its collector to thereby yieldan output RF signal (RF_out) of the PA.

In some embodiments, the foregoing example PA configuration of FIG. 3Bcan be depicted as two or more stages as shown in FIG. 3C. The firststage 64 a can be configured as, for example, a driver stage; and thesecond stage 64 b can be configured as, for example, an output stage.

FIG. 3D shows that in some embodiments, a PA can be configured as aDoherty PA. Such a Doherty PA can include amplifying transistors 64 a,64 b configured to provide carrier amplification and peakingamplification of an input RF signal (RF_in) to yield an amplified outputRF signal (RF_out). The input RF signal can be split into the carrierportion and the peaking portion by a splitter. The amplified carrier andpeaking signals can be combined to yield the output RF signal by acombiner.

FIG. 3E shows that in some embodiments, a PA can be implemented in acascode configuration. An input RF signal (RF_in) can be provided to abase of the first amplifying transistor 64 a operated as a commonemitter device. The output of the first amplifying transistor 64 a canbe provided through its collector and be provided to an emitter of thesecond amplifying transistor 64 b operated as a common base device. Theoutput of the second amplifying transistor 64 b can be provided throughits collector so as to yield an amplified output RF signal (RF_out) ofthe PA.

In the various examples of FIGS. 3A-3E, the amplifying transistors aredescribed as bipolar junction transistors (BJTs) such as heterojunctionbipolar transistors (HBTs). It will be understood that one or morefeatures of the present disclosure can also be implemented in or withother types of transistors such as field-effect transistors (FETs).

FIG. 4 shows that in some embodiments, the amplification system 52 ofFIG. 2 can be implemented as a high-voltage (HV) power amplificationsystem 70. Such a system can include an HV power amplifier assembly 54configured to include HV amplification operation of some or all of thePAs (e.g., 60 a-60 c). As described herein, such PAs can be biased by abias system 56. In some embodiments, the foregoing HV amplificationoperation can be facilitated by an HV supply system 58. In someembodiments, an interface system 72 can be implemented to provideinterface functionalities between the HV power amplifier assembly 54 andeither or both of the bias system 56 and the HV supply system 58.

A power amplifier (PA) often includes an output power array havingmultiple semiconductor devices operating in parallel. While it isdesirable to have each of the individual devices operate at exactly thesame condition, imperfections between devices, as well as temperaturegradients across the array, can cause variations in their operatingpoints. Under extreme conditions, one of the devices may thermallyrun-away causing the power array to collapse, and thereby resulting inpermanent failure. Such a problem becomes more complex when operating athigh supply voltages since more power dissipation is introduced in thearray.

Described herein are examples related to use of a cascode amplifierstructure to decouple performance-degrading thermal protection solutionsfrom high performance radio-frequency (RF) power array elements.

In some applications, thermal ruggedness can be built into an array byincreasing distances between devices in the power array, and by throughballasting techniques. Such techniques can introduce local feedback ateach of the devices within the power array.

Spreading of the array can reduce the heating of adjacent array elementsand can effectively reduce the thermal resistance of the array to heatsinking structures. Such a technique can result in an increased area forthe array, and can also increase the corresponding die size and cost.

Ballasting techniques are often in the form of emitter degeneration orbase degeneration. These solutions can introduce loss in the RF signalpath which can degrade gain, efficiency and saturated power, therebyreducing performing. Other solutions which utilize a cascodearchitecture may include a common connection of the cascode emitters,which typically involves ballasting of the cascode devices to preventthermal run-away.

Described herein are one or more features related to cascode PAarchitectures that can operate at higher supply voltages. Such highersupply voltage operation can compound thermal issues, since the powerper unit area tends to increase with increasing voltage. Takingadvantage of the higher supply voltage, a cascode PA architecture can besegmented such that each individual power array element has an isolatedconnection to its associated cascode element. The resulting structurecan force a majority of the supply voltage and power dissipation acrossthe cascode element, and can reduce the maximum voltage across the RFpower device to, for example, less than 1V. The low voltage across theRF device can reduce or eliminate the requirement for ballasting, whilethe individual connection of the cascode device can provideself-ballasting functionality for the cascode array to thereby preventor reduce thermal run-away.

In some embodiments, a cascode PA architecture having one or morefeatures as described herein can be implemented so as to reduce thearray footprint of a power array while maintaining high gain. Since thehigh power dissipation is placed across the cascode device which isself-ballasted due to the individual connections, these devices can beplaced closer together than other configurations, and yet require lessballasting of the RF array devices.

FIG. 5A shows an example array 90 in which a plurality of cascodeddevices 92 are arranged in parallel, and having ballasting of cascodesegments and increased ballasting of RF array to prevent currentcrowding and thermal run-away. Such a configuration results in thecascoded devices being coupled as indicated by 94.

FIG. 5B shows the same example array 90 of FIG. 5A. In FIG. 5B, anexample collector current path 96 is depicted. Such a collector currentcan be experienced during a thermal run-away event. In such an event,substantially all of the collector current could go through a singlecommon base transistor (e.g., the upper right transistor), therebydamaging the transistor.

FIG. 6 shows an example of an isolated cascode array 100 that can beconfigured to force more even distribution of collector current acrossall of the common base transistors. Accordingly, likelihood of damagecan be reduced or eliminated during a thermal run-away event.

In FIG. 6, each cascoded device is indicated as 102. FIG. 7 shows a moredetailed example of such a cascoded device, and FIG. 8 shows how aplurality of such cascoded devices can be arranged so as to form anarray.

In the example of FIG. 7, a cascoded device 102 is shown to include acommon emitter (CE) device 110 (also referred to herein as an RFtransistor) coupled to a common base (CB) device 112 (also referred toherein as a cascode transistor). The emitter of the RF transistor 110 isshown to be coupled to the base of the cascode transistor 112 through acascode bypass capacitance C2.

The base of the RF transistor 110 is shown to be coupled to an RFballast resistance R2. In turn, the RF ballast resistance R2 is coupledto a node 126. A bias input 120, an RF input 122, and a second harmonicinput 124 are coupled in parallel with node 126. As shown in FIG. 7, thebias input 120 is coupled to the node 126 through DC ballast resistanceR1, the RF input 122 is coupled to the node 126 through DC blockcapacitance C1, and the second harmonic input 124 is coupled to the node126 through the capacitance C3. R1, C1, C3, the node 126, R2, and inputs120, 122, 124 are collectively referred to as an input bias circuit 140for ease of reference.

The base of the cascode transistor 112 is shown to be coupled to a biasinput 130 in series with a cascode ballast resistance R3, which arecollectively referred to as a cascode bias circuit 150 for ease ofreference. The emitter of the RF transistor 110 can be coupled to ground128, and the collector of the cascode transistor 112 can be coupled to asupply voltage node 132.

FIG. 8 shows an example of an array 100 having two cascoded devices 102,102′ arranged so as to provide isolation property. Each cascoded deviceis similar to the example of FIG. 7. It will be understood that morethan two cascoded devices can be arranged in a similar manner.

In the example array 100 of FIG. 8, each cascoded device can include itsown bias circuits for the RF transistor and the cascode transistor. Moreparticularly, the RF transistor 110 of the first cascoded device 102 isshown to have a input bias circuit 140 coupled to its base, and thecascode transistor 112 is shown to have a cascode bias circuit 150coupled to its base. Similarly, the RF transistor 110′ of the secondcascoded device 102′ is shown to have an input bias circuit 140′ coupledto its base, and the cascode transistor 112′ is shown to have a cascodebias circuit 150′ coupled to its base.

In the example of FIG. 8, at least some portions of the input biascircuits 140, 140′ can be coupled to facilitate, for example, a commonRF input. Similarly, the collectors 132, 132′ of the cascode transistors112, 112′ can be coupled to yield a common RF output, and to receive acommon supply voltage.

In some embodiments, the array of cascoded devices of FIG. 8 can beimplemented so as to yield isolated connections between the parallelelements. For example, the array can be built with a plurality of CE(110)/CB (112) pairs, instead of building a separate CE array and aseparate CB array.

FIG. 9 shows an example layout 200 of a CE/CB pair and relatedconnections to form a cascoded device. The example layout 200 is similarand adapted from the example of the cascoded device 102 in FIG. 7. Sucha pair, when combined with other pair(s), can yield the foregoingisolation functionality. Various parts and connections are shown and/orindicated in FIG. 9. It will be understood that the layout 200 is onlyan example; and that other layouts can be implemented.

FIG. 10 shows an example layout 210 of two CE/CB pairs and relatedconnections to form cascoded devices similar to the example of FIG. 8.The example layout 210 is similar and adapted from the example of thearray 100 of two cascoded devices 102, 102′ in FIG. 8. As shown in FIG.10, the two CE/CB pairs are combined in parallel similar to the cascodeddevices 102, 102′ in FIG. 8. Various parts and connections are shownand/or indicated in FIG. 10. It will be understood that the layout 210is only an example; and that other layouts can be implemented.

FIG. 11 shows an example layout 220 in which 18 CE/CB pairs are arrangedin a two-dimensional array and electrically connected in parallel. Inthe example shown, some of the CB transistors (112), which are thehigher power devices, and he CE transistors (110) are highlighted. Asshown in FIG. 11, a first CE/CB including CB 112 and CE 110 is combinedin parallel to a second CE/CB pair including CB 112′ and CE 110′ in aregion 130. Similarly, a third CE/CB pair including CB 112″ and CE 110″is combined in parallel to a fourth CE/CB pair including CB 112′″ and CE110′″ in a region 130′.

In the example of FIG. 11, the area occupied by CB transistor 112 is 160μm², and the area occupied by CE transistor 110 is 40 μm². In theexample of FIG. 11, the distance between the centers of CB 112 and CB112′ in region 130 is 55 μm, and the distance between the center of CB112′ in region 130 and the center of CB 112″ in region 130′ is 70 μm. Inthe example of FIG. 11, the distance between the centers of CB 112 andCB 112″″ is 155 μm. It will be understood that various values areexamples only; and that other values can be implemented. It will also beunderstood that other numbers of pairs and other two-dimensionalcombinations can be implemented.

FIG. 12 shows temperature-rise curves as a function of device spacing.At the closest device spacing of about 55 μm (in FIG. 11), thetemperature increase is shown to be about 4° C. The curves in FIG. 12assumes 3000 μW/μm² power dissipation density in a cascode device.Actual power dissipation density in the cascode device is about 200μW/μm²; accordingly, the temperature increase is expected to be evenless.

FIGS. 13 and 14 show performance plots of amplitude-to-amplitude (AM-AM)distortion and amplitude-to-phase (AM-PM) distortion, respectively, atvarious operating conditions of the array of cascoded devices. FIG. 15shows performance plots of collector efficiency and power addedefficiency (PAE) as a function of output power at similar operatingconditions of the array of cascoded devices. FIG. 16 shows an enlargedview of the performance plots of FIG. 15. FIG. 17 shows performanceplots of adjusted channel leakage ratio 1 (ACLR1) as a function ofoutput power at similar operating conditions of the array of cascodeddevices. FIG. 18 shows an enlarged view of the performance plots of FIG.17. FIG. 19 shows performance plots of ACLR2 as a function of outputpower at similar operating conditions of the array of cascoded devices.For the foregoing plots in FIGS. 13-19, the example array of cascodeddevices is operated with a supply voltage of approximately 10V.

FIG. 20 shows that in some embodiments, one or more features associatedwith a cascode architecture as described herein (e.g., the array 100 inFIGS. 6, 8, 10, and 11) can be implemented in a radio-frequency (RF)module. Such a module can be, for example, a front-end module (FEM). Inthe example of FIG. 20, a module 300 can include a packaging substrate302, and a number of components can be mounted on such a packagingsubstrate. For example, a front-end power management integrated circuit(FE-PMIC) component 304, a power amplifier assembly 306, a matchcomponent 308, and a duplexer assembly 310 can be mounted and/orimplemented on and/or within the packaging substrate 302. Othercomponents such as a number of surface mount technology (SMT) devices314 and an antenna switch module (ASM) 312 can also be mounted on thepackaging substrate 302. In some implementations, the power amplifierassembly 306 includes the array 100 shown in FIGS. 6, 8, 10, and 11.Although all of the various components are depicted as being laid out onthe packaging substrate 302, it will be understood that somecomponent(s) can be implemented over other component(s).

In some implementations, a device and/or a circuit having one or morefeatures described herein can be included in an RF device such as awireless device. Such a device and/or a circuit can be implementeddirectly in the wireless device, in a modular form as described herein,or in some combination thereof. In some embodiments, such a wirelessdevice can include, for example, a cellular phone, a smart-phone, ahand-held wireless device with or without phone functionality, awireless tablet, etc.

FIG. 21 depicts an example radio-frequency (RF) device 400 having one ormore advantageous features described herein. In the context of a modulehaving one or more features as described herein, such a module can begenerally depicted by a dashed box 300, and can be implemented as, forexample, a front-end module (FEM). Such a module can include an array100 of cascoded devices as described herein.

Referring to FIG. 21, a power amplifier array 100 can receive theirrespective RF signals from a transceiver 410 that can be configured andoperated in known manners to generate RF signals to be amplified andtransmitted, and to process received signals. In some implementations,the power amplifier array 100 is similar to and adopted from the array100 shown in FIGS. 6, 8, 10, and 11. The transceiver 410 is shown tointeract with a baseband sub-system 408 that is configured to provideconversion between data and/or voice signals suitable for a user and RFsignals suitable for the transceiver 410. The transceiver 410 can alsobe in communication with a power management component 406 that isconfigured to manage power for the operation of the RF device 400. Insome implementations, the power management component 406 can alsocontrol operations of the baseband sub-system 408 and the module 300.

The baseband sub-system 408 is shown to be connected to a user interface402 to facilitate various input and output of voice and/or data providedto and received from the user. The baseband sub-system 408 can also beconnected to a memory 404 that is configured to store data and/orinstructions to facilitate the operation of the wireless device, and/orto provide storage of information for the user.

In the example RF device 400, outputs of the PA array 100 are shown tobe matched (via respective match circuits 422) and routed to theirrespective duplexers 424. Such amplified and filtered signals can berouted to an antenna 416 through an antenna switch 414 for transmission.In some embodiments, the duplexers 424 can allow transmit and receiveoperations to be performed simultaneously using a common antenna (e.g.,416). In FIG. 21, received signals are shown to be routed to “Rx” paths(not shown) that can include, for example, a low-noise amplifier (LNA).

In some implementations, the RF device 400 is a wireless device such asa cellular phone, laptop, tablet, wearable computing device, or thelike. A number of other wireless device configurations can utilize oneor more features described herein. For example, a wireless device doesnot need to be a multi-band device. In another example, a wirelessdevice can include additional antennas such as diversity antenna, andadditional connectivity features such as Wi-Fi, Bluetooth, and GPS.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense, as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to.” The word “coupled”, as generally usedherein, refers to two or more elements that may be either directlyconnected, or connected by way of one or more intermediate elements.Additionally, the words “herein,” “above,” “below,” and words of similarimport, when used in this application, shall refer to this applicationas a whole and not to any particular portions of this application. Wherethe context permits, words in the above Description using the singularor plural number may also include the plural or singular numberrespectively. The word “or” in reference to a list of two or more items,that word covers all of the following interpretations of the word: anyof the items in the list, all of the items in the list, and anycombination of the items in the list.

The above detailed description of embodiments of the invention is notintended to be exhaustive or to limit the invention to the precise formdisclosed above. While specific embodiments of, and examples for, theinvention are described above for illustrative purposes, variousequivalent modifications are possible within the scope of the invention,as those skilled in the relevant art will recognize. For example, whileprocesses or blocks are presented in a given order, alternativeembodiments may perform routines having steps, or employ systems havingblocks, in a different order, and some processes or blocks may bedeleted, moved, added, subdivided, combined, and/or modified. Each ofthese processes or blocks may be implemented in a variety of differentways. Also, while processes or blocks are at times shown as beingperformed in series, these processes or blocks may instead be performedin parallel, or may be performed at different times.

The teachings of the invention provided herein can be applied to othersystems, not necessarily the system described above. The elements andacts of the various embodiments described above can be combined toprovide further embodiments.

While some embodiments of the inventions have been described, theseembodiments have been presented by way of example only, and are notintended to limit the scope of the disclosure. Indeed, the novel methodsand systems described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes in theform of the methods and systems described herein may be made withoutdeparting from the spirit of the disclosure. The accompanying claims andtheir equivalents are intended to cover such forms or modifications aswould fall within the scope and spirit of the disclosure.

What is claimed is:
 1. A power amplifier comprising: a plurality ofpairs of transistors, each pair of transistors including a commonemitter transistor and a common base transistor arranged in a cascodeconfiguration; and electrical connections implemented to connect theplurality of pairs in a parallel configuration between an input node andan output node, the electrical connections configured to distribute acollector current to all of the common base transistors to therebyreduce likelihood of damage to one or more common base transistorsduring a thermal run-away event.
 2. The power amplifier of claim 1wherein, for each of the plurality of pairs of transistors, the emitterof the common emitter transistor is coupled to the base of the commonbase transistor through a bypass capacitance.
 3. The power amplifier ofclaim 1 wherein, for each of the plurality of pairs of transistors, thebase of the common emitter transistor is coupled to an input biascircuit.
 4. The power amplifier of claim 3 wherein the input biascircuit includes a radio-frequency (RF) ballast resistance.
 5. The poweramplifier of claim 3 wherein the input bias circuit of the plurality ofpairs of transistors are coupled a common RF input.
 6. The poweramplifier of claim 1 wherein, for each of the plurality of pairs oftransistors, the emitter of the common emitter transistor is coupled toa ground potential.
 7. The power amplifier of claim 1 wherein, for eachof the plurality of pairs of transistors, the base of the common basetransistor is coupled to a cascode bias circuit.
 8. The power amplifierof claim 7 wherein the cascode bias circuit includes a cascode ballastresistance.
 9. The power amplifier of claim 1 wherein, for each of theplurality of pairs of transistors, a collector of the common basetransistor is coupled to a supply voltage.
 10. The power amplifier ofclaim 1 wherein the collectors of the common base transistors of theplurality of pairs of transistors are coupled to yield a common RFoutput.
 11. A radio-frequency (RF) module comprising: a packagingsubstrate configured to receive a plurality of components; and a poweramplification system implemented on the packaging substrate, the poweramplification system including a power amplifier (PA) configured toreceive and amplify an RF signal, the PA including a plurality of pairsof transistors, each pair of transistors including a common emittertransistor and a common base transistor arranged in a cascodeconfiguration, the PA further including electrical connectionsimplemented to connect the plurality of pairs in a parallelconfiguration between an input node and an output node, the electricalconnections configured to distribute a collector current to all of thecommon base transistors to thereby reduce likelihood of damage to one ormore common base transistors during a thermal run-away event.
 12. The RFModule of claim 11 wherein, for each of the plurality of pairs oftransistors, the emitter of the common emitter transistor is coupled tothe base of the common base transistor through a bypass capacitance. 13.The RF Module of claim 11 wherein, for each of the plurality of pairs oftransistors, the base of the common emitter transistor is coupled to aninput bias circuit.
 14. The RF Module of claim 11 wherein, for each ofthe plurality of pairs of transistors, the base of the common basetransistor is coupled to a cascode bias circuit.
 15. A radio-frequency(RF) device comprising: a transceiver configured to generate an RFsignal; a front-end module (FEM) in communication with the transceiver,the FEM including a packaging substrate configured to receive aplurality of components, the FEM further including a power amplifier(PA) configured to and amplify the RF signal, the PA including aplurality of pairs of transistors, each pair of transistors including acommon emitter transistor and a common base transistor arranged in acascode configuration, the PA further including electrical connectionsimplemented to connect the plurality of pairs in a parallelconfiguration between an input node and an output node, the electricalconnections configured to distribute a collector current to all of thecommon base transistors to thereby reduce likelihood of damage to one ormore common base transistors during a thermal run-away event; and anantenna in communication with the FEM, the antenna configured totransmit the amplified RF signal.
 16. The RF device of claim 15 whereinthe RF device includes a wireless device.
 17. The RF device of claim 16wherein the wireless device includes a cellular phone.
 18. The RF deviceof claim 15 wherein, for each of the plurality of pairs of transistors,the emitter of the common emitter transistor is coupled to the base ofthe common base transistor through a bypass capacitance.
 19. The RFdevice of claim 15 wherein, for each of the plurality of pairs oftransistors, the base of the common emitter transistor is coupled to aninput bias circuit.
 20. The RF device of claim 15 wherein, for each ofthe plurality of pairs of transistors, the base of the common basetransistor is coupled to a cascode bias circuit.